The present invention broadly relates to a sail-rig with a mast for sail-craft, and more specifically, to a sail rig for sailboards, with which an unstayed, non-braced mast is connected by means of a fully-articulated, rotating and pivoting joint.
Modern sail-craft are practically always equipped with a triangular main sail connected along its luff to as stiff as possible a mast, and whose clew is attached to the rear end of a boom, which is held at its forward end by the mast. Many small sail-craft, such as dinghies, Lasers and sailboards have neither jib sails nor mast stays. The masts of these so-called cat-type rigs can be subject to extreme forces. Even while setting the sail, the requisite preloading causes the mast to deflect considerably and under the influence of wind forces the sail's tensile force causes increased mast deflection. On account of this, the sail shape changes unfavorably, thereby reducing desirable forward thrust while unwanted side forces increase.
In order to keep the undesirable mast deformation within acceptable limits, it has been common practice to use masts with large cross-sections. A thick mast along the leading edge affects aerodynamic efficiency quite unfavorably, not only by slowing down the air flow but also by creating turbulence, which in turn destroys the suction on the leeward sail side, which is supposed to provide most of the thrust. It is known that in such a case aerodynamic drag increases by more than 50% and lift is reduced by about 20%. This means that forward thrust is dramatically reduced.
In order to avoid these disadvantages there has been a move towards thinner masts, with the attendant disadvantage of more undesirable mast deflection. Where large sail-craft re concerned, the problem of this mast deflection under high wind forces is solved with stays and bracing. However, additional aerodynamic drag and turbulence is created by these measures.
The connection between wishbone boom and mast of conventional sailboards represents an enormous local or point stress, which is proven by the fact that most mast breakages usually occur at or near that location. In order to absorb the high leverage forces, unstayed masts need not only a sufficiently thick profile or cross-section but also need to be made of strong materials. As a result, they are aerodynamically inefficient, expensive and heavy.